As used herein, the term “volcanic plume” or “volcanic ash plume” means a cloud of volcanic ash, the term “volcanic gases” means gases given off by active volcanoes, and the term “gas plume” means a plume of a volcanic gas. Dispersed volcanic gases disposed outside the volume occupied by a volcanic ash plume are not included as part of the “volcanic ash plume” as the latter term is used herein.
Volcanic ash can pose a hazard to flying jet aircraft, threaten the health of people and livestock, damage electronics and machinery, and interrupt power generation and telecommunications. Volcanic ash comprises tiny jagged particles of rock and natural glass blasted into the air by a volcano. Wind can carry ash thousands of miles, affecting far greater areas than other volcano hazards.
Volcanic plumes present two problems for aircraft: (a) engine malfunction due to ash; and (b) aircraft damage and/or crew and passenger injury due to ash and corrosive gases. Volcanic ash particles are extremely abrasive. They are jagged particles of rock and glass that can cause rapid wear to the internal workings of jet engines. More important, high temperatures in some parts of jet engines can melt ash that is passed through an engine. The ash then re-solidifies on cooler parts of the engine, forming a layer that blocks airflow, interferes with moving parts, and eventually causes malfunction of the engine. It is therefore desirable for aircraft to be capable of detecting volcanic ash prior to encountering the ash or as quickly as possible thereafter to avoid prolonged exposure to the ash.
Various known solutions for detecting and avoiding a volcanic plume during flight of an aircraft have certain disadvantages. First, for volcanoes that are well monitored, sensors or people on the ground can quickly observe an eruption and report it to flight safety authorities such as the FAA. In these cases, a notice to airmen is issued. However, many remote volcanoes around the world are still not well instrumented and can erupt without immediate detection. Even after detection, the mechanism to issue a notice to airmen imposes a delay for processing and distribution, during which an unwarned aircraft may encounter the plume.
Second, a few satellites are capable of detecting volcanic plumes from orbit, based on the sulfur dioxide spectra, the thermal infrared emission, visible ash clouds, or a combination of these. When a satellite detects a volcanic plume, a notice to airmen is issued. However, satellite observations are not continuous. An eruption that occurs between satellite passes may go undetected for 6 to 12 hours, which is more than enough time for aircraft to encounter the plume. The period of non-detection may go on longer for small eruptions or during overcast conditions. Even after detection, the mechanism to issue a notice to airmen imposes a delay for processing and distribution, during which an unwarned aircraft may encounter the plume.
Third, in daytime clear weather, pilots can visually observe a distinctive volcanic plume and avoid it. Visual observation may be done with the naked eye or with cameras using natural light, infrared emission, optical backscatter measured via lidar or optical backscatter using standard aircraft light sources. Airborne ash particles are exposed and able to reflect light or emit infrared radiation. However, volcanic plumes are often encountered during nighttime and/or embedded within other clouds, such as meteorological clouds containing water droplets or ice crystals, rendering visual detection methods ineffective. In this description, water droplets and ice crystals will be referred to collectively herein as “water precipitate” or “precipitate” for conciseness, and the term “precipitate particles” will refer to droplets of water or crystals of ice embedding ash particles. Meteorological clouds not only surround a volcanic plume, but, because the individual ash particles serve as nucleation sites for precipitate particles, the individual ash particles become embedded in precipitate particles. Therefore, the ash particles are not visible and contribute almost nothing to the electromagnetic signature of the cloud.
Typical uses of infrared emission to detect volcanic plumes use sensors directed toward the natural atmosphere. For example, U.S. Pat. No. 5,654,700, entitled “Detection System for Use in an Aircraft,” proposes a system that would detect a volcanic ash cloud ahead of an aircraft by monitoring infrared radiation that traverses the ash cloud. However, the optical and infrared signatures of ash particles that are embedded in precipitate particles are camouflaged and remain hidden from such infrared sensors.
If volcanic ash is not detected, the first sign to an aircraft crew that the aircraft has flown through a water vapor cloud containing volcanic ash is engine failure. A typical pilot response when an engine begins to fail is to increase power. However, when volcanic ash is present, this could make the situation worse. If ash is suspected as the cause of an engine failure, then a pilot may throttle back engines, turn on engine and wing anti-ice devices and lose height to drop below the ash cloud as soon as possible. This action typically helps to restore engine functionality. However, because the aircraft may have already flown through a substantial amount of ash, aircraft parts may have already suffered costly damage which may require maintenance, repair or replacement of engine parts. Therefore, avoiding any amount of flight time through ash helps to reduce any potentially damaging effects of the ash, and therefore helps to save maintenance time and money.
There exists a need for a system that will detect volcanic plumes embedded in clouds and ash particles embedded in precipitate particles, and alert an aircraft to avoid such volcanic plumes, or to rapidly change course to escape such volcanic plumes.